A century ago, we imagined futuristic cities full of hulking, steel buildings, their towers surrounded by a lace of elevated roads. But today, the future of architecture is biology. Synthetic biology architects and designers imagine cities that are made from bioengineered materials, fed by energy from sunlight. These cities sometimes look more like forests than metropolises. Here are a few visions of the living cities of tomorrow.

Famed architect Frank Lloyd Wright toyed with the idea of a "living city" which would be a perfect balance of urban modernism and natural beauty. Here is one of his sketches of such a city from the 1950s.

In this image called "The Advent of Yellowstone," the artist imagines a city in Yellowstone Park, "when humans develop eco-friendly technology to develop cities without harming the environment." The Swordsman77 on Deviant Art

This city by J. Humphries on Deviant Art is made out of reclaimed space ship parts that have been turned into tree houses on an alien world. Just because we go to other plants doesn't mean we should stop using recycled materials.